[OpenType] Getting more than 65535 glyphs per font

John Hudson john at tiro.ca
Sun Feb 14 20:58:18 CET 2010

Khaled Hosny wrote:

> With virtual fonts you can do all sorts
> of glyph remapping and composite fonts and even inter-font interaction
> (e.g. kerning between glyphs from different real fonts).

The current thinking on the composite font standard (CFS) is that it 
would not enable cross-font glyph processing, e.g. no kerning between 
glyphs from different component fonts and no GSUB or GPOS interaction. 
This was decided during early discussion of the project, but it is 
something that continues to niggle at me.

I think the most common situation that will potentially cause problems 
-- which I described during that early discussion -- will be interaction 
with punctuation, e.g. kerning between a letter glyph in a secondary 
component font and punctuation from the primary component font (the CFS 
format has a concept of primary font, which among other things provides 
glyphs for common characters such as punctuation, numerals, etc.) This 
situation is addressable by rolling punctuation into runs with adjacent 
script characters, so that the punctuation glyphs come from the same 
component font, and are subject to glyph processing. But one is left 
with text with varying forms of punctuation, which might look odd, 
especially in situations where, for example, text in quotations begins 
in one script but ends in another.

I can understand the reasoning against defining cross-font glyph 
processing interaction in the CFS format. It is much easier if the 
composite font can pass glyph strings to existing layout support as if 
they were from individual fonts. But while the decision has been to 
avoid cross-font glyph processing now, I would like to see the format 
defined in such a way that it would be possible to extend in this 
direction in future.



Tiro Typeworks        www.tiro.com
Gulf Islands, BC      tiro at tiro.com

Car le chant bien plus que l'association d'un texte
et d'une mélodie, est d'abord un acte dans lequel
le son devient l'expression d'une mémoire, mémoire
d'un corps immergé dans le mouvement d'un geste
ancestral.  - Marcel Pérès

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